Multiple telephony switching systems, such as private branch exchanges (PBXs), are often configured such that one or more of them can take over communications processing for another of them. This is generically referred to herein as a “failover” arrangement. Failover arrangements are usually implemented for reliability, that is, to ensure continuity of communications capability should one of the switches fail. Failover arrangements can take many forms, but a common form is the active/standby mode wherein two or more switches are duplicated, at least one of them is active and processing calls, and at least another one of them is standing by ready to take over for the active switch. The duplicated switches may be co-located and therefore can share communications trunks that connect them to the public switched telephone network (PSTN). However, this does not protect the entity—e.g., a business or an agency—served by the switches against loss of communications capability due to the location itself becoming unusable, such as in the case of a disaster. Therefore, the duplicated switches typically are geographically separated (located at different locations) in order to provide continuity of communications capability should one of the locations become unusable. In this case, the duplicated switches can no longer share trunks, and they rely on the PSTN to redirect communications that would normally be directed to one (the formerly-active) location to the other (the formerly-standby) location.
If the active switch fails, the failure is detected and the redirection is effected automatically by the PSTN. But there are situations where the entity served by the switches may wish to have the redirection effected voluntarily even though the active switch has not failed. For example, the entity may wish to have the redirection effected because of an emergency, a practice drill, or building maintenance at the location of the active switch. One way of effecting voluntary redirection is to have the communications administrator of the entity served by the switches re-administer call routing on the active switch in order to force the redirection. But, administration is time consuming, and also complex and hence prone to errors. Therefore, re-administration is not a good solution during emergencies. Another way of effecting voluntary redirection is provided as a service by the PSTN. This service (referred to in the trade as Custom Redirect Service, Switched Redirect Service, or Disaster Routing Service) allows the communications administrator or other representative of the entity served by the PBX switches to contact its service provider in the PSTN and request redirection, which is then effected by the service. CRS is a tariffed service which incurs an additional cost to the entity requesting a redirect service. The CRS service is tariffed on a call-by-call basis, and so the cost can mount up quickly. Another disadvantage is that the served entity has to contact the service provider to obtain the service, which introduces another level of administration.